1. Field of the Invention
The present invention relates to a mixed catalyst and a method for producing an unsaturated acid or an unsaturated nitrile using the mixed catalyst.
2. Description of the Related Art
Conventionally, a method for subjecting propylene or isobutylene to a vapor-phase catalytic oxidation reaction or a vapor-phase catalytic ammoxidation reaction to produce a corresponding unsaturated carboxylic acid or unsaturated nitrile has been well known. In recent years, attention has been directed to a method for subjecting propane or isobutane in place of propylene or isobutylene to a vapor-phase catalytic oxidation or a vapor-phase catalytic ammoxidation to produce a corresponding unsaturated carboxylic acid or unsaturated nitrile.
Hitherto, various oxide catalysts have been proposed as a catalyst used for the vapor-phase catalytic ammoxidation. Although an oxide obtained by mixing and calcining molybdenum and vanadium or the like as necessary is generally used as a catalyst as it is, a technique for further subjecting the calcined catalyst to a post-treatment in producing an unsaturated carboxylic acid or an unsaturated nitrile has also been studied.
For example, Japanese Patent Laid-Open No. 10-028862 discloses a technique for impregnating a Mo—V—Sb/Te-based catalyst with a solution containing one or more elements selected from the group consisting of tungsten, molybdenum, chromium, zirconium, titanium, niobium, tantalum, vanadium, boron, bismuth, tellurium, palladium, cobalt, nickel, iron, phosphor, silicon, rare-earth elements, alkali metals, and alkali earth metals.
Japanese Patent Laid-Open No. 2008-062231 discloses a technique for bringing a mixed metal oxide catalyst into contact with water, and optionally an aqueous metal oxide precursor to produce a modified mixed metal oxide, and calcining the obtained modified mixed metal oxide.
Japanese Patent Laid-Open No. 2006-077557 discloses a technique for immersing tungsten and manganese in a Mo—V—Sb—Nb-based catalyst.
International Publication WO 2009-048553 discloses a technique for mixing a catalyst with a modifier such as an antimony compound, a molybdenum compound, a tellurium compound, and a tungsten compound, and subjecting the obtained catalyst to a reaction, or mixing a catalyst or a catalyst precursor with a modifier, calcining the obtained mixture, and subjecting the calcined product to a reaction.
However, when the present inventors used the oxide catalysts disclosed in Japanese Patent Laid-Open No. 10-028862, Japanese Patent Laid-Open No. 2008-062231, and Japanese Patent Laid-Open No. 2006-077557 for the vapor-phase catalytic oxidation or the vapor-phase catalytic ammoxidation reaction of propane or isobutane, all the catalysts provided an insufficient yield of the target product.
The producing methods described in Japanese Patent Laid-Open No. 10-028862, Japanese Patent Laid-Open No. 2008-062231, Japanese Patent Laid-Open No. 2006-077557, and International Publication WO 2009-048553 describe improvement in performance of the Mo—V—Te/Sb-based composite oxide having activity as it is by impregnating the composite oxide with tungsten or immersing tungsten in the composite oxide. However, the composite oxide before the impregnation or the immersion does not contain tungsten, and a catalyst providing a high yield of the target product has not yet been obtained.
In view of the above-mentioned situation, it is an object of the present invention to provide a mixed catalyst for a vapor-phase catalytic oxidation or a vapor-phase catalytic ammoxidation reaction of propane or isobutane, capable of providing a corresponding unsaturated acid or unsaturated nitrile at high yield from propane or isobutane. It is another object of the present invention to provide a method for producing an unsaturated acid or an unsaturated nitrile using the mixed catalyst.